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Old 28th Nov 2021, 6:49 pm   #41
murphyv310
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Default Re: HMV 2807 Restoration

Hi.
Here are some more pictures of the results. I'm using my old Fuji here that doesn't focus too well but at least I can adjust the shutter.
I get the slight feeling the CRT has lost a little emission over night, hopefully I'm wrong.
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Old 28th Nov 2021, 7:04 pm   #42
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Default Re: HMV 2807 Restoration

Full 3MHz bandwidth! Ah! you can't beat these old EMI sets.

Peter
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Old 28th Nov 2021, 8:13 pm   #43
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Default Re: HMV 2807 Restoration

Quote:
Originally Posted by murphyv310 View Post
I get the slight feeling the CRT has lost a little emission over night, hopefully I'm wrong.
Mains voltage down with the cold?

Steve
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Old 28th Nov 2021, 8:27 pm   #44
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Default Re: HMV 2807 Restoration

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Originally Posted by Panrock View Post
Quote:
Originally Posted by murphyv310 View Post
I get the slight feeling the CRT has lost a little emission over night, hopefully I'm wrong.
Mains voltage down with the cold?

Steve
Good point Steve, in retrospect I did have to increase the height!
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Old 28th Nov 2021, 10:34 pm   #45
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Default Re: HMV 2807 Restoration

Quote:
I'll do a video for authenticity and show the top of the cabinet to prove its a real Royal set
By appointment to his Majesty King George VI, I assume!
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Old 28th Nov 2021, 11:30 pm   #46
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Quote:
I'll do a video for authenticity and show the top of the cabinet to prove its a real Royal set
By appointment to his majesty king george VI, I assume!
Absolutely.
Of course like all or most of HMVs products of the time.
This one came up from Retrotech this year, would be interesting to know a little of its history.
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Old 29th Nov 2021, 12:24 am   #47
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Default Re: HMV 2807 Restoration

The intermediate frequencies in the HMV 2807 and Marconi VT73DA are 34mc/s vision and 37.5mc/s sound, not far away from the later BREMA frequencies of 34.65mc/s and 38.15mc/s.
Rather than aligning the vision IFs for double sideband, the vision receiver is aligned for single sideband operation which helps to reduce the bandwidth considerably and yet allows for the full video frequencies to be displayed.
Hence those 3meg bars visible on the test card.
Trevor's wise choice of replacement decoupling capacitors ensured the IF amplifier works it would have when the set was new.
The attachment shows the alignment chart for the superhet models 2807 and 3807.
I assume "Northern" is the Holm Moss transmitter on channel B2.

DFWB.
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Old 29th Nov 2021, 9:24 am   #48
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Default Re: HMV 2807 Restoration

Quote:
Originally Posted by murphyv310 View Post
Quote:
Originally Posted by McMurdo View Post
Quote:
I'll do a video for authenticity and show the top of the cabinet to prove its a real Royal set
By appointment to his majesty king george VI, I assume!
Absolutely.
Of course like all or most of HMVs products of the time.
This one came up from Retrotech this year, would be interesting to know a little of its history.
Great restoration job on the HMV 2807. I sold the set at Retrotech and I bought it about 20 years ago at a Drayton Manor radio rally. Unfortunately I don't have any more information on its history.

Steve
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Old 29th Nov 2021, 9:31 am   #49
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Default Re: HMV 2807 Restoration

Hi Steve.
Many thanks for the reply to the thread.
Well at least that's 20 years of its history accounted for and now a good result. The cabinet is in pretty good shape and worm free which is unusual for HMV.
The set won't be run that often as we want to preserve the CRT for as long as possible.
Thanks for the information and your kind words.
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Old 29th Nov 2021, 3:50 pm   #50
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Default Re: HMV 2807 Restoration

Hello All

As a proud member of the HMV 1807/2807 appreciation society I thought you might like to see this which I found 1807A instructions and receipt.

I hope my IT department (SWMBO) has done a good enough job so the small print can be read. Even in early 1950 the number of addenda is quite surprising!

The attached receipt is a real document of its age when civility and service were paramount.

Hope you find it interesting

Steve

Have got to do 3 posts this is 1/3
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Old 29th Nov 2021, 3:53 pm   #51
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Default Re: HMV 2807 Restoration

HMV1807/2807

Steve

2/3
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Old 29th Nov 2021, 3:53 pm   #52
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Default Re: HMV 2807 Restoration

HMV1807/2807

Steve

3/3
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Old 30th Nov 2021, 12:06 am   #53
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Default Re: HMV 2807 Restoration

Hi Steve.
Many thanks for sharing those interesting documents.
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Old 3rd Dec 2021, 3:20 pm   #54
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Default Re: HMV 2807 Restoration

Hi Trevor,
I'm only now catching up with the story of your HMV 2807 restoration.
I've really enjoyed the read. I'm always impressed when people take on these beasties. I quite like the look of these sets, particularly the consoles, however the high chance of tube difficulties had always put me off restoring one myself.
I'm glad you were able to get a good tube for yours.
It sad just how bad these sets were. I used to own an HMV 1804 and it was excellent, though clearly somewhat dated for its time.
I imagine that if you had owned an EMI set before the war and then gone on to purchase an HMV 1807 when they came out, you would have been a very unhappy customer.

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Old 3rd Dec 2021, 5:50 pm   #55
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Default Re: HMV 2807 Restoration

Some while back I carried out an experiment employing an HMV 1807, Bush TV12A and a Ferguson 941T all from 1949.
I ran them all from a common variac making sure that their voltage selectors were set for 250V.
All was well from the start with 250V applied but it was interesting to note what happened when the input was slowly reduced. Around 230 V the Ferguson and Bush were still working well but the HMV was showing signs of being unhappy. Both line and frame hold required adjustment together with picture height and focus.
At 220V the HMV had thrown the towel in. The focus was out of range of the control and the timebases were very troubled. At 210V the picture vanished.
It is interesting to note that the Ferguson and Bush worked down to 215V with little bother. Just a tweak on the height and brilliance brought back a picture of good entertainment value.
At this time [1940s/50s the mains stability was at it's worst with load shedding and a generally variable supply. This is where the 1807 series failed. Owners constantly fiddled with the nasty preset controls and it must have been a nightmare to keep the dim out 3/16 in focus with around 4KV to focus the picture.
Add to this all the horrible decoupling capacitors and cheap resistors and you had a disaster waiting to happen. These days we have a stable 240V [it is actually around 248 at my address] and capacitors of a quality that would have been unimaginable in 1949. The MOV valve line up, the worst being the B36 double triode that were never two the same did nothing to encourage hope It didn't improve much with later models and I'm not surprised EMI ceased television production in 1957. Both the public and the dealers had had enough. Of course there were good ones and a 12SN7 replacing the B36 helps a lot. John.
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Old 3rd Dec 2021, 5:55 pm   #56
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Default Re: HMV 2807 Restoration

Quote:
I imagine that if you had owned an EMI set before the war and then gone on to purchase an HMV 1807 when they came out, you would have been a very unhappy customer.
I have restored 3 sets with the 1807 chassis, they all had the common problems, such as low emission tubes, O/C slider pots, awful EMI capacitors,
Poor quality B36 & Z77 valves etc.

They do work surprisingly well with modern components fitted, but way behind the reliability & performance of Bush & Pye sets of the time.
The cabinets are the usual good quality expected from HMV, the LOPT is a good quality item, as is the mains dropper.

I am amazed Trevor managed to find a good 3/16, rarer than a dodo!
It is incredible how many sets have survived, especially the console models, it was not uncommon for the CRT to fail within a year, the 10" version really was the worst CRT ever made, but Mazda came a close second with the CRM92.....


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Old 3rd Dec 2021, 7:17 pm   #57
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Default Re: HMV 2807 Restoration

Hi.
Thanks Mark & John. Today I noticed the HT was 242v after the mains energised speaker and a whopping 259 after the rectifier. I actually thought there was a hidden BY127 somewhere but no it still has the original selenium rectifier! A 33 ohm 7 watt was added in to get the HT to around 225v, this was with a mains feed of 238v AC. After adding the resistor only a small adjustment to the frame hold was required. After I did the mod I wondered if the reason for the high HT is the use of a 30P19 instead of the KT36, I think I'll pop it back in tomorrow and compare the HT or total current drawn off the HT.
I also today decided the feed the CRT heaters externally (they are 8v in this set) and pass a current between Grid and cathode in the same way as Bertha does. This type of cathode cleaning is very gentle so long as you don't go wild with heater current as these Emiscope tubes have very delicate heaters. To start with I could only achieve around 400ua but within a few minutes we were over 1.2ma then it stabilised, at that point HT was removed and the heaters left on for a further few minutes.
The result is now less flaring and good overall focus, its no brighter but much nicer to watch.
It's now in the house upstairs ready for the Queens speech.
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Old 11th Dec 2021, 4:40 pm   #58
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Default Re: HMV 2807 Restoration

Thinking about it, back in the late 40's when the regulation of the mains supply was so poor I'm surprised the chassis was not fitted with a type 304 Barretter manufactured by MOV/GEC. This would have overcome much of the problems encountered due to mains voltage variations. I don't think EMI were very happy about the production of any AC/DC receivers. John.
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